Download 1.2 Atomic Structure

1.2 Atomic Structure
Learning outcomes
• Matter is composed of particles, which
may be atoms, molecules or ions.
• Atoms. Minute size of atoms.
• Law of conservation of mass.
DIFFUSION- evidence for the
existence of small particles
• SPREADING OUT OF GASES
• COLOUR OF INK SREADING OUT
WHEN MIXED WITH WATER
• HYDROGEN CHLORIDE AND AMMONIA
SOLUTION
AMMONIUM CHLORIDE
HISTORY OF THE ATOM
• GREEKS – MATTER MADE OF TINY
INDIVISIBLE PARTICLES
DALTON 1766-1844
• ALL MATTER MADE OF SMALL
PARTICLES CALLED ATOMS
• ATOMS ARE INDIVISIBLE
• ATOMS CANNOT BE CREATED OR
DESTROYED
DISCOVERY OF THE
ELECTRON
• CROOKES CONDUCTED
EXPERIMENTS WITH A GLASS TUBE
CROOKES TUBE
CROOKES TUBES
• CATHODE CONNECTED TO NEGATIVE
ELECTRODE
• ANODE CONNECTED TO THE
POSITIVE ELECTRODE
• CNAP
VACUUM TUBES
• GAS AT LOW PRESSURE
• ELECTRIC CURRENT PASSED
THROUGH
• RADIATION CAME FROM THE END OF
THE TUBE CONNECTED TO THE
NEGATIVE(CATHODE) END OF THE
BATTERY
• CATHODE RAYS
TUBES
CROOKES PADDLE TUBE
CATHODE RAYS
•
•
•
•
CAST SHADOWS
CAUSE GLASS TO GLOW
TURN A PADDLE WHEEL
RAYS ARE MADE OF PARTICLES
JJ THOMPSON
• HOLE IN ANODE TO
ALLOW BEAM OF
RAYS TO PASS
THROUGH.
• BEAM COULD BE
DEFLECTED BY
ELECTRIC PLATES.
• THEREFORE BEAM IS
MADE OF NEGATIVE
PARTICLES.
JJ THOMPSONS APPARATUS
JJ THOMPSON
• USED A MAGNETIC FIELD FROM AN
ELECTROMAGNET TO DEFLECT THE
ELECTRONS
• CALCULATED THE RATIO OF CHARGE
TO MASS FOR ELECTRON
GEORGE STONEY
• NAMED PARTICLES ELECTRONS
ROBERT MILLIKAN
• FAMOUS OIL-DROP EXPERIMENT
• IT MEASURED THE CHARGE ON THE
ELECTRON
• X-RAYS IONISED AIR MOLECULES BY
STRIPING ELECTRONS OFF THEIR ATOMS.
• OIL DROPLETS PICKED UP ELECTRONS
BECAME NEGATIVE
• INCREASED THE + CHARGE UNTIL THE
DROPLET HOVERED.
• TOOK MEASUREMENTS AND CALCULATED
THE CHARGE ON THE ELECTRON.
ROBERT MILLIKAN
ROBERT MILLIKAN
THOMPSON’S ATOM
• ATOM A SPHERE OF POSITIVE
CHARGES WITH NEGATIVE ELECTONS
EMBEDDED
ERNEST RUTHERFORD
• FIRED THIN ALPHA PARTICLES AT A
TIN GOLD FOIL
• THOMPSONS PLUM PUDDING MODEL
PREDICTED THAT THEY WOULD PASS
THRU’ WITH LITTLE DEFLECTION
RUTHERFORD’S EXPT
•
RUTHERFORD’S EXPT
EXPECTED RESULT
• ALPHA PARTICLES SHOULD PASS
THROUGH WITH LITTLE DEFLECTION
+
++
ACTUAL RESULT
• MOST PASS THROUGH UNDEFLECTED
• SOME BOUNCED RIGHT BACK!
EXPLANATION
• HARD DENSE CORE OF POSITIVE
MATTER IN THE CENTER OF EACH
ATOM-NUCLEUS
• ATOMS ARE MOSTLY EMPTY SPACE.
THE PROTON
• RUTHERFORD CONTINUED TO
BOMBARD DIFFERENT ELEMENTS
SUCH AS NITROGEN AND OXYGEN
• SMALL POSITIVE PARTICLES WERE
GIVEN OFF--- PROTONS
THE NEUTRON
• JAMES CHADWICK BOMBARDED
BERYLLIUM WITH ALPHA PARTICLES.
• SMALL PARTICLES WERE GIVEN OFF
WHICH WERE NEUTRAL AND HAD THE
SAME MASS AS THE PROTON—THE
NEUTRON.
Bohr’s atom
• Electrons
travel in
orbits
around the
nucleus
Learning Outcomes
• Properties of electrons,
protons and neutrons
(relative mass, relative
charge, location within
atom).
Proton
• Protons are
positively
charged
particles
found within
atomic
nucleus
Learning Outcomes
Atomic number (Z ), mass number (A),
isotopes; hydrogen and carbon as
examples of isotopes.
Relative atomic mass (A r). The
12C scale for relative atomic
masses.
Atomic number
• Also called
proton
number, this
is the number
of protons the
atom has
Atomic number
• Also called
proton
number, this
is the number
of protons the
atom has
The Number of Electrons
• Atoms must have equal
numbers of protons and
electrons. In our example, an
atom of krypton must contain
36 electrons since it contains
36 protons.
Mass number
•Mass Number =
(Number of Protons) +
(Number of Neutrons)
Isotope
• Atoms that have the same
number of protons but different
numbers of neutrons are
called isotopes
Hydrogen isotopes
• The element hydrogen for
example, has three
commonly known isotopes:
protium, deuterium and
tritium
Deuterium
•an atom of deuterium
consists of one proton
one neutron and one
electron
Tritium
• An atom of tritium
consists of one proton
two neutrons and one
electrons
Relative Atomic Mass
• The relative atomic mass
of an element the mass of
one of the element's atoms - relative to the mass of an
atom of Carbon 12,
Learning Outcomes
• Calculation of approximate relative atomic
masses from abundance of isotopes of
given mass number (e.g. Calculation of
approximate relative atomic mass of
chlorine).
Chlorine
•Chlorine-35 and
Chlorine-37 are both
isotopes of chlorine
Relative mass of chlorine
• Chlorine consists of roughly
75% Chlorine-35 and roughly
25% Chlorine-37. We take an
average of the two figures The
relative atomic mass of
chlorine is usually quoted as
35.5.
Learning outcomes
• Use of the mass spectrometer in determining
relative atomic mass.
• Fundamental processes that occur in a mass
spectrometer:
• vaporisation of substance,
• production of positive ions,
• acceleration, separation,
• detection (mathematical
• treatment excluded).
THE MASS SPECTROMETER
• Atoms can be deflected by
magnetic fields - provided the
atom is first turned into an ion.
Stage 1: Ionisation
• The atom is ionised by
knocking one or more
electrons off to give a
positive ion.
Stage 2: Acceleration
• The ions are accelerated so
that they all have the same
kinetic energy.
Stage 3: Deflection
• The ions are then deflected by
a magnetic field according to
their masses. The lighter they
are, the more they are
deflected.
Stage 4: Detection
• The beam of ions
passing through the
machine is detected
electrically.